Volvo fm adblue problem

emmisions high comes on when engine not pulling or going down small grade,after a short while pulling light stays on then goes out altogether stays like this for a week or few days then as soon as I go down grade or coast on it comes again,spent 400 quid so far and getting a bit sick, been in volo main dealer and I think they are only guiseing please help

What fault codes do you have?